The expression and control of bioregulatory macromolecules in embryo-fetal development and the effects of their interactions on cellular proliferation, differentiation and immunocompetence are investigated and compared to related growth factors of tumor-cell origin. Comparative examination of an antiviral activity in placental extracts from several inbred strains of mice demonstrated the presence of an interferon (MuIFN-Pl) exhibiting common characteristics in the placentas of all seven strains examined. NuIFN-Pl exhibits a species specific antiviral activity requiring a cellular transcriptional event and has antiproliferative characteristics. The kinetics of development and decay of the MuIFN-Pl induced antiviral state is time-dependent. MuIFN-Pl activity in placentas is maximal at term and is composed of two distinct species that function synergistically in their induction of the antiviral state in vitro. Both species, however, are biologically and serologically distinguishable from classical mouse interferons alpha, beta and gamma. Trypsin-collagenase dispersed placental cells concentrating at the 20-30 and 30-40 per cent Percoll gradient interfaces are the major producers of interferon and represent less than 2 per cent of the total cell population. Applications of an in vitro induction system for antibody precursor cells has been used to generate a series of IgM producing hybridomas against purified TGF that directly abrogate TGF-induced mitogenesis in mouse cells.